Preparation method of starch edible film containing thyme essential oil emulsion

Abstract

The invention relates to a starch edible film of thyme essential oil emulsion and a preparation method thereof. The starch edible film of thyme essential oil emulsion comprises the following components: cassava starch solution, thyme essential oil emulsion, glycerol and water. The starch edible film of the thyme essential oil emulsion prepared by the preparation method disclosed by the invention not only can improve the encapsulation efficiency of the essential oil and the stability of the emulsion, but also can realize slow release of the essential oil, and meanwhile, the mechanical property of the starch edible film is improved, so that the film is more flexible, and the film has antioxidant and antibacterial properties.

Description

Technical Field

[0001] The invention belongs to the field of food packaging materials, and particularly relates to a method for preparing an edible starch film containing thyme essential oil emulsion. Background Art

[0002] As a natural polymer, starch is abundant in source, low in cost, easy to modify, good in film-forming property, renewable and pollution-free. It is one of the most promising natural biodegradable materials. Starch-based edible film is not only green, environmentally friendly, safe and healthy, but also can improve food quality and protect food from moisture migration, microbial growth and nutrient oxidation.

[0003] Adding functional compounds to the film can make it have bioactive functions such as antibacterial and antioxidant functions, thereby broadening and improving the applicability and application of the film. However, adding essential oils alone is prone to problems such as uneven dispersion and rapid release. Therefore, encapsulating the essential oils can not only make the essential oils evenly distributed, but also achieve controlled release and other effects, thereby extending the shelf life of the food. Summary of the invention

[0004] The purpose of the present invention is to provide a new material and method that can improve the material properties of traditional starch films and stably protect loaded active substances.

[0005] The purpose of the present invention is achieved by the following technical means:

[0006] The first aspect of the present invention provides a thyme essential oil emulsion starch edible film, comprising the following components: tapioca starch, thyme essential oil emulsion, glycerin and water.

[0007] Preferably, the thyme essential oil emulsion comprises zein, sodium caseinate, thyme essential oil and water.

[0008] Preferably, in the thyme essential oil emulsion, the zein accounts for 1% of the total volume of the emulsifier, and the sodium caseinate accounts for 1% of the total volume of the emulsifier.

[0009] Preferably, in the thyme essential oil emulsion, the thyme essential oil content accounts for 30%-70% of the total volume.

[0010] Preferably, the tapioca starch accounts for 3%-7% of the total volume, the glycerol accounts for 20%-60% of the starch mass, and the thyme essential oil emulsion accounts for 1%-5% of the total volume; further preferably, the tapioca starch accounts for 5% of the total volume, the glycerol accounts for 40% of the starch mass, and the thyme essential oil emulsion accounts for 3% of the total volume.

[0011] The second aspect of the present invention provides a method for preparing an edible film of thyme essential oil emulsion starch, comprising the following steps:

[0012] S1, dispersing cassava starch into distilled water, heating and stirring to obtain a mixture A;

[0013] S2, adding thyme essential oil emulsion into mixture A;

[0014] S3, adding glycerol, and then stirring to obtain a mixture B;

[0015] S4, subjecting the mixture B to ultrasonic treatment at room temperature for 30 min to remove bubbles and obtain a film-forming liquid;

[0016] S5. Pour the film-forming liquid completely onto a polytetrafluoroethylene plate and dry it at 50°C to form a film.

[0017] Preferably, the thyme essential oil emulsion in step S2 is prepared by the following method:

[0018] R1. Disperse zein and sodium caseinate separately in distilled water and stir at 600 rpm for at least 2 h to ensure hydration.

[0019] R2, then the dispersed zein solution and sodium caseinate solution were mixed in a mass ratio of 1:1, and stirred at 600 rpm for 30 min to obtain a suspension;

[0020] R3, adding thyme essential oil drop by drop into the suspension prepared in step R2, and continue stirring;

[0021] R4, homogenizing the emulsion obtained in step R3 by a high-speed homogenizer at a speed of 12000 rpm, and finally obtaining a thyme essential oil emulsion;

[0022] Preferably, the thyme essential oil content accounts for 30%-70% of the total volume of the emulsion.

[0023] Preferably, the method for preparing the thyme essential oil emulsion starch edible film comprises the following steps:

[0024] Step 1: At room temperature, zein and sodium caseinate are dispersed in distilled water and stirred at 600 rpm for at least 2 h to ensure hydration.

[0025] Step 2: Subsequently, at room temperature, the dispersed zein solution and sodium caseinate solution were mixed in a mass ratio of 1:1, and stirred at 600 rpm for 30 minutes to obtain a suspension.

[0026] Step 3: Add thyme essential oil dropwise into the suspension prepared in step 2, and continue stirring at a speed of 400 rpm.

[0027] Step 4: homogenize the emulsion obtained in step 3 by a high-speed homogenizer at a speed of 12000 rpm for 4 min to finally obtain a thyme essential oil emulsion.

[0028] Step 5, dispersing cassava starch in distilled water and heating and stirring at 90°C for 30 minutes to obtain a mixture A. The emulsion obtained in step 4 was added to the mixture A in different proportions, followed by adding glycerol, and then stirring for 20 minutes to obtain a mixture B; the mixture B was ultrasonicated at room temperature for 30 minutes to remove bubbles to obtain a film-forming liquid; finally, the film-forming liquid was completely poured on a polytetrafluoroethylene plate and dried at 50°C for 6 hours to form a film.

[0029] Compared with the prior art, the present invention has the following advantages:

[0030] The invention provides a simple, quick and good performance edible starch film, the required ingredients of which are easily available and low in cost.

[0031] The invention enables the starch film to have antibacterial and antioxidant activities by adding thyme essential oil active substances.

[0032] The invention adds the emulsion loaded with thyme essential oil into the starch film, thereby improving the stability and encapsulation rate of the essential oil and making the active substance have a good slow release effect.

[0033] The thyme essential oil emulsion starch edible film prepared by the invention can be used for preserving fruits and vegetables and prolonging the shelf life of fruits and vegetables. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 Effect of different concentrations of thyme essential oil on the storage stability of emulsions

[0035] Figure 2 Appearance of edible starch film containing different concentrations of thyme essential oil emulsion

[0036] Figure 3 Effects of different concentrations of thyme essential oil emulsions on the optical properties of edible starch films DETAILED DESCRIPTION

[0037] The present invention is further described in detail below in conjunction with the examples, but the embodiments of the present invention are not limited thereto. The raw materials involved in the present invention can be purchased directly from the market. For process parameters not specifically noted, conventional techniques can be used.

[0038] Example 1: Preparation and testing of thyme essential oil emulsion

[0039] Experimental methods First, 2g of zein and sodium caseinate were dispersed in 100ml of distilled water at room temperature and stirred at 600rpm for at least 2h to ensure hydration. Then, the dispersed zein solution and sodium caseinate solution were mixed at a mass ratio of 1:1 and stirred at 600rpm for 30min to obtain a suspension. Thyme essential oil (30%-70%, v / v) was added dropwise into the suspension, and stirring was continued at 400rpm. Finally, it was homogenized at 12000rpm for 4min by a high-speed homogenizer to finally obtain an oil-in-water emulsion containing 30%-70% thyme essential oil.

[0040] 1.1. Thyme essential oil emulsion was subjected to the following storage stability test

[0041] The emulsion samples were stored at room temperature (20°C). The foaming stability of the emulsion samples was monitored by visually observing the height of the water phase formed at the bottom of the bottle. Photos were taken 1 day, 7 days, 15 days, and 30 days after the samples were prepared.

[0042] 1.2. Thyme essential oil emulsion was tested for encapsulation efficiency as follows

[0043] Take 10 μL of thyme essential oil, dilute to 10 mL with 95% ethanol, shake well, then prepare 0.02, 0.025, 0.03, 0.035, 0.04, 0.045, 0.05 ul / mL from the 10 mL, dilute to 10 mL with 95% ethanol and shake well, draw a thyme essential oil standard curve with thyme essential oil concentration as the horizontal axis and absorbance value as the vertical axis.

[0044] Take 1 ml of the emulsion and mix it with 3 ml of n-hexane, vortex and oscillate for 30 seconds, extract the unencapsulated free essential oil with n-hexane, centrifuge at 10000 rpm / min for 10 minutes, dilute the supernatant appropriately, measure its absorbance value, and calculate the essential oil concentration by the standard curve. The encapsulation rate is calculated by the following formula:

[0045] EE(%)=C0-C1C0×100

[0046] In the formula, C0 and C1 represent the amount of original essential oil added to the emulsion (μg / mL) and the content of free essential oil (μg / mL), respectively.

[0047] 1.3. Thyme essential oil emulsion is tested for particle size as follows

[0048] The size of the emulsion droplets was measured by using a laser scattering particle size distribution analyzer (Model SYNC, Mackinac, USA). To avoid multiple scattering effects in the measurement, the refractive index of water and temperature were set to 1.33 and 25 °C, respectively, and at least three batches of emulsions were measured. To prevent the experimental results from being affected, the thyme essential oil emulsion was diluted 50 times with deionized water before the emulsion particle size was measured.

[0049] Experimental Results

[0050] like Figure 1 As shown, after 30 days of storage, the water phase of the emulsions loaded with 30% and 40% thyme essential oil precipitated; while the emulsion loaded with 50% thyme essential oil had good stability, was milky white, and had no water phase precipitation; although the emulsions loaded with 60% and 70% thyme essential oil had no water phase precipitation, they showed different degrees of oil phase, among which the emulsion loaded with 70% thyme essential oil showed the most obvious phase separation.

[0051] Table 1 Particle size and encapsulation efficiency of thyme essential oil emulsion loaded with 30%-70%

[0052]

[0053] As shown in Table 1, the initial average particle size of the emulsion loaded with 30% thyme essential oil is 5.77±0.45μm. With the increase of thyme essential oil, the particle size of the emulsion shows a rule of first decreasing and then increasing. When loaded with 50% thyme essential oil, the emulsion shows a minimum particle size of 3.22±0.21μm, and then the particle size of the emulsion increases to 34.8±4.59μm (70% thyme essential oil) and presents a multimodal distribution; this is due to the aggregation and precipitation of oil droplets, and the encapsulation efficiency is also low at this time (69.27±3.23%). When the thyme essential oil increases from 30% to 50%, the encapsulation efficiency increases from 75.28±1.33% to 90.9±0.78%. In summary, the emulsion with thyme essential oil encapsulated by zein and sodium caseinate as emulsifiers can have good loading capacity and stability.

[0054] Taking into account the emulsion stability and loading capacity, 50% thyme essential oil can be preferentially selected as the oil phase to prepare the water-in-oil emulsion.

[0055] Example 2: Preparation and testing of thyme essential oil emulsion starch edible film

[0056] Experimental methods: Tapioca starch (5%, w / v) was dispersed in distilled water and heated and stirred at 90°C for 30 min to fully gelatinize the starch, and then an emulsion loaded with 50% thyme essential oil was added to the starch solution, followed by glycerol (40%, w / w, based on dry starch weight) and stirred for 20 min. The mixed solution was ultrasonicated at room temperature for 30 min to remove bubbles to obtain a film-forming solution, and finally the film-forming solution was completely poured on a polytetrafluoroethylene plate and dried at 50°C for 6 h to form a film. The edible film prepared in the control group was not added with thyme essential oil emulsion.

[0057] 1.1. The mechanical properties of thyme essential oil emulsion starch edible film were tested as follows

[0058] First, the average thickness of the film was measured using a digital micrometer (Casio, Mainland China). Five points were randomly selected for testing with a resolution of 0.001 mm. A TA.XTPlusC texture analyzer was used to determine the tensile strength (TS, MPa) and elongation at break (EAB, %) of the film. The composite film was cut into strips (1×5 cm). It was then pretreated in a sealed dryer for 48 hours at room temperature (25±1°C). The film was loaded into the test system, and the tensile strength was calculated by dividing the maximum load by the cross-sectional area of ​​the film. The elongation at break is expressed as the percentage change in the original length of the specimen between two clampings at the time of fracture.

[0059]

[0060] In the formula, F represents the maximum stress at break; b represents the film width; d represents the film thickness; ΔG represents the stretched length; and G represents the initial length.

[0061] 1.2. Thyme essential oil emulsion starch edible film was subjected to the following water vapor permeability test

[0062] Use a mortar to grind CaCl2 into a powder with uniform particle size, dry it in an oven to completely remove its moisture, cool it to room temperature, and place about 2g of CaCl2 powder in a 40mm×25mm weighing bottle. Select a flat, wrinkle-free, hole-free film, cut it into a circle slightly larger than the mouth of the weighing bottle, measure its thickness with a handheld thickness gauge, and then seal the sample film at the mouth of the bottle with paraffin, and weigh it with an electronic balance with an accuracy of 0.1mg. Place the weighed weighing bottle in a dryer at room temperature and 100% RH (the relative humidity is provided by pure water). After balancing for 2 hours, take it out and weigh it every hour until the mass change between two adjacent times is less than 5% The experiment ends. Calculate the water vapor permeability (MVP) of the film using the following formula:

[0063]

[0064] In the formula, Δm represents the mass increment in the time period t, in g; t represents the time interval, in s; δ represents the thickness of the sample film, in m; A represents the surface area of ​​the sample film, in m 2 ; ΔP is expressed as the saturated water vapor pressure difference on both sides of the membrane, unit KPa.

[0065] 1.3. The optical properties of thyme essential oil emulsion starch edible film were tested as follows

[0066] The sample was cut into a 3 cm × 1 cm rectangle and attached to the inside of a cuvette. The transmittance of the sample film in the wavelength range of 200 nm to 800 nm was measured using a UV-2600 ultraviolet-visible spectrophotometer. The opacity of the film (mm) was calculated by dividing the absorbance at 600 nm by the film thickness (mm). -1 ).

[0067] 1.4. The antibacterial properties of thyme essential oil emulsion starch edible film were tested as follows

[0068] The antimicrobial activity of the films against Escherichia coli and Staphylococcus aureus was determined using a disk diffusion test. The films, cut into 6 mm discs, were sterilized under UV light and then placed in a Petri dish containing NB agar, which had been inoculated with 0.1 ml of a diluted inoculum (105-106 CFU / ml). The antimicrobial activity was evaluated by measuring the growth inhibition zone (diameter in mm). For comparison, the films were used as negative controls to determine the antimicrobial activity.

[0069] 1.5. The antioxidant properties of thyme essential oil emulsion starch edible film were tested as follows

[0070] The antioxidant activity of the film was evaluated by ABTS and DPPH free radical scavenging assays. The film was immersed in distilled water and then shaken at 150 rpm for 1 hour at 25°C and centrifuged at 3000g for 10 minutes to remove undissolved materials to prepare a 2.0% (w / v) film extract. Then, 0.05 mL of the film extract solution was mixed with 5.95 mL of ABTS reagent. The mixture was placed in the dark for 10 minutes and the absorbance at a wavelength of 734 nm was measured. In the DPPH assay, a mixture containing 1 mL of the film extract solution and 3 mL of the DPPH reagent was kept in the dark for 1 hour before measuring the absorbance at 517 nm.

[0071] Experimental Results

[0072] like Figure 2As shown, both the control film and the starch film with added emulsion have good flexibility and gloss, presenting a smooth and uniform surface. As the emulsion content increases, the opacity value of the starch film increases, which indicates that the loaded essential oil emulsion can provide a certain barrier for the film and can maximize the preservation of packaged food.

[0073] Table 2 Thickness, mechanical properties, water vapor permeability and opacity value of starch edible films containing different concentrations of emulsion

[0074]

[0075] As shown in Table 2, tensile strength and elongation at break can both represent the mechanical properties of the film. Tensile strength refers to the maximum stress that a material can withstand before breaking, expressing the toughness and strength of the material; elongation at break reflects the extension properties of the material and can be used to express the flexibility or plasticity of the material. Adding essential oil emulsion to the starch edible film significantly reduces the TS of the film and improves the EAB, thereby reducing the hardness of the film and improving the elasticity of the film.

[0076] As shown in Table 2, the initial water vapor permeability of the control starch film was 3.19 ± 0.21 × 10 -7 g / (m·s·KPa). With the addition of essential oil emulsion, the water vapor permeability can be reduced to 2.66±0.17×10 -7 g / (m·s·KPa). This is because the protein has good hydrophobicity, which is conducive to forming an entangled network in the film, thereby forming a moisture-proof layer. It may also be related to the particle size of the emulsion, providing good barrier properties.

[0077] like Figure 3 As shown in the figure, compared with the starch edible film without adding essential oil emulsion, the UV-visible light transmittance of the starch film loaded with essential oil emulsion is significantly reduced, and the transmittance at 600nm is reduced from 40.09% to 1.39%. In addition, in the range of 200-300nm, the UV transmittance of the essential oil emulsion film is almost zero, indicating that the addition of essential oil emulsion can effectively protect food from UV deterioration.

[0078] Table 3 Comparison of antioxidant properties of starch edible films containing different concentrations of emulsion

[0079]

[0080] As shown in Table 3, the antioxidant activity of starch film without essential oil emulsion was the lowest. When different concentrations of essential oil emulsion were added, the starch film showed good antioxidant activity. When 3% of essential oil emulsion was added, the DPPH free radical scavenging rate increased from 12.52±1.33% to 61.20±2.12%, and the ABTS scavenging activity increased from 14.06±1.46% to 64.54±1.51%. This was mainly due to the decrease in droplet size. When the amount of essential oil emulsion added increased to 5%, the antioxidant capacity decreased. On the one hand, the reason was the increase in emulsion particle size, and on the other hand, it was due to the volatilization of essential oil during storage. These DPPH and ABTS antioxidant test results show that at the optimal concentration of essential oil emulsion, the essential oil retention rate is higher, resulting in a good antioxidant effect.

[0081] Table 4 Comparison of antibacterial properties of starch edible films containing different concentrations of emulsion

[0082]

[0083] As shown in Table 4, no inhibitory activity was detected in the film of the control group. With the increase of the concentration of essential oil emulsion, the inhibitory activity was significantly enhanced. When the addition amount of essential oil emulsion was 3%, the starch film had the strongest inhibitory activity, and the inhibition zone diameters of Escherichia coli and Staphylococcus aureus were 34.10±0.30mm and 37.20±0.45mm, respectively. However, compared with the starch film containing 3% essential oil emulsion, the inhibitory ability of the starch film containing 4% and 5% emulsion decreased, which was mainly due to the flocculation of the emulsion on the surface of the starch film, which caused the essential oil to volatilize easily during storage. Therefore, adding 3% essential oil emulsion has good antibacterial activity against Escherichia coli and Staphylococcus aureus.

[0084] The above embodiments are only preferred implementation modes of the present invention and are only used to explain the present invention rather than to limit the present invention. Any changes, substitutions, modifications, etc. made by those skilled in the art without departing from the spirit of the present invention should fall within the scope of protection of the present invention.

Claims

1. An edible starch film containing thyme essential oil emulsion, characterized in that: It includes the following ingredients: tapioca starch, thyme essential oil emulsion, glycerin, and water.

2. A starch edible film containing thyme essential oil emulsion according to claim 1, characterized in that, The thyme essential oil emulsion comprises zein, sodium caseinate, thyme essential oil and water.

3. A starch edible film containing thyme essential oil emulsion according to claim 2, characterized in that, In the thyme essential oil emulsion, the thyme essential oil accounts for 30%-70% of the total volume.

4. A starch edible film containing thyme essential oil emulsion according to claim 3, characterized in that, In the thyme essential oil emulsion, the thyme essential oil accounts for 50% of the total volume.

5. A starch edible film containing thyme essential oil emulsion according to claim 2, characterized in that, In the thyme essential oil emulsion, the zein accounts for 2% and the sodium caseinate accounts for 2%.

6. The edible starch film containing thyme essential oil emulsion according to claim 1, characterized in that: The cassava starch accounts for 5%, the glycerol accounts for 40% of the dry weight of the starch, and the thyme essential oil emulsion accounts for 1-5%.

7. A method for preparing an edible starch film containing thyme essential oil emulsion, characterized in that: The following steps are involved: S1, dispersing cassava starch into distilled water, heating and stirring to obtain a mixture A; S2, adding thyme essential oil emulsion into mixture A; S3, adding glycerol, and then stirring to obtain a mixture B; S4, subjecting the mixture B to ultrasonic treatment at room temperature for 30 min to remove bubbles and obtain a film-forming liquid; S5. Pour the film-forming liquid completely onto a polytetrafluoroethylene plate and dry it at 50°C to form a film.

8. The method for preparing a starch edible film containing thyme essential oil emulsion according to claim 7, characterized in that: The thyme essential oil emulsion in step S2 comprises the following steps: R1. Disperse zein and sodium caseinate separately in distilled water and stir at 600 rpm for at least 2 h to ensure hydration. R2, then the dispersed zein solution and sodium caseinate solution were mixed in a mass ratio of 1:1, and stirred at 600 rpm for 30 min to obtain a suspension; R3, adding thyme essential oil drop by drop into the suspension prepared in step R2, and continue stirring; R4, homogenizing the emulsion obtained in step R3 by a high-speed homogenizer at a speed of 12000 rpm, and finally obtaining a thyme essential oil emulsion.

9. The method for preparing a starch edible film containing thyme essential oil emulsion according to claim 8, characterized in that: The thyme essential oil content accounts for 30%-70% of the total volume.

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